1. Field of the Invention
The present invention relates to a system-on-panel typed liquid crystal display, and more particularly, a system-on-panel including active layers of single crystalline silicon for use with a driver, a controller, and a central processing unit.
2. Description of the Related Art
Liquid crystal display (hereinafter LCD) panels are flat-panel displays which are used in a variety of products, including consumer electronics, computers, and communication terminals.
When liquid crystal displays are used, a subsystem comprising the drivers for driving the data and the gate lines, a controller for controlling the LCD, and a central processing unit (hereinafter CPU) circuit for controlling the controller and performing the arithmetic and logic processes, is generally required. The controller and the CPU circuit are often comprised of a CPU, ROMs, RAMs, oscillators and resistors.
The structure of an LCD display panel is a simple one. The liquid crystal is encapsulated between two glass substrates, a TFT substrate, and a color-filter/common electrode substrate. That is, the TFT and the color-filter/common electrode substrates are two parallel sheets of glass with liquid crystal injected between them.
More specifically, LCD panels may include: (1) a lower plate on which a plurality of unit cells comprised of switching devices, such as TFTs and picture elements (hereinafter pixels) are arranged; (2) an upper plate comprising color filters, also called the common electrode substrate; (3) liquid crystal injected between these two plates; (4) a polarizing plate which polarizes visible light between the plates; and (5) a backlight for supplying light from one of the plates.
The transparent common electrode on the upper plate/substrate can be made of ITO (Indium Tin Oxide), and is deposited on top of the color filter substrate. In order to obtain good display quality, the cell gap of the liquid-crystal (i.e., the spacing between the two glass substrates) has to be precisely controlled to a specific value. This gap has to be uniform over the whole display area and reproducible from one end to the other. Therefore, transparent spacers, such as plastic beads, are placed on the surface of the glass substrates.
Furthermore, a transparent insulating glass substrate that is pervious to light, is used. Normally, two layers of insulators are formed on a gate electrode. Insulating substrates are used because when light strikes the semiconductor layer, the resulting photoelectric conversion produces a current, thus increasing the amount of off-current. This can cause malfunction in the case of LCD panels. To prevent this problem, the semiconductor layer is completely shielded from light. Another reason for using insulating substrates is for protection of the semiconductor layer during the manufacturing process of other layers such as when drain and source electrodes are formed so that the semiconductor is protected from structural and physical damage.
LCD panels are manufactured under low temperature conditions in order to protect the glass substrates from damage because glass has a relatively large specific gravity and is weakened and brittle when heated.
FIGS. 1A–1C show various types of LCDs. In FIG. 1A, an LCD according to a first related art which uses amorphous silicon thin film transistor (hereinafter TFT) deposited on a glass substrate 100 as the switching device of choice for the pixel array shown.
However, in this situation, the driver in an LCD is required to perform very fast switching operations. Forming the switches using amorphous silicon TFTs is not an appropriate method in order to achieve quick switching operations in an efficient manner. Instead, the use of silicon chips formed by fabricating metal oxide silicon transistors (hereinafter MOS transistors) on silicon wafers attached to a glass substrate 100 where pixels for the LCD have been formed is more desirable. Subsequently, the controller for controlling the drivers and the CPU circuit may be provided by a separate phase of the manufacturing process.
As illustrated in FIG. 1B, a new technique of forming polycrystalline silicon (hereinafter p-Si) under low temperature conditions has been developed. Polycrystalline silicon TFTs are easily fabricated on glass substrates using a number of manufacturing techniques. One of such techniques proposed involves laser crystallization for forming polycrystalline silicon by depositing amorphous silicon on a glass substrate under low temperature conditions and, successively, by scanning the amorphous silicon with a laser beam.
The above-proposed technique enables fabrication of an LCD having a built-in driver because the pixel array comprising the TFT switches and the drivers are directly formed on the glass substrate 100. Unfortunately, a controller made of single crystalline silicon and a CPU circuit are provided by separate processes and on a separate substrate.
In FIG. 1C, another technique for manufacturing a system-on-panel (hereinafter SOP) is shown. This technique enables fabrication of an LCD by mounting a CPU circuit and a controller, comprised of a CPU, ROMs, RAMS, and oscillators on a glass substrate. Accordingly, by forming pixels as an image display and a driver on the glass substrate 100 and mounting a controller, and a CPU circuit to control the pixels on the glass substrate 100, it is possible to fabricate a portable LCD product which is significantly improved in terms of reduced weight and size.
FIG. 2 shows a cross-sectional view of an SOP typed LCD according to a Japanese Publication No. 8-313935. In this cross-sectional illustration, an aluminum layer 2 having patterns corresponding to drain/source wires and contact wires of a CPU circuit oriented in the y-direction is deposited on a glass substrate 1 by sputtering. Next, a polycrystalline silicon layer 3 for a source/drain region is formed by Low Pressure Chemical Vapor Deposition (hereinafter LPCVD). A P+ layer or an N+ layer is formed by doping the p-Si layer 4 with impurity ions, such as boron (B) or phosphorus (P). Another p-Si layer 4 of an active layer is formed on the P+ or the N+ layer by LPCVD. After the p-Si layer 4 has been activated by thermal treatment, a gate insulating silicon oxide layer 5 is formed.
Thereafter, the following layers are formed successively: (1) an aluminum (hereinafter Al) layer 6 comprising the gate electrodes; (2) an Al wire 7 oriented in the y-direction; (3) a mounting pad 8 for a CPU, RAM, ROM, and IC; (4) a lead attachment pad 9; and (5) a bare-chip mounting pad 8 for the resistors, capacitors, oscillators and connectors.
A color filter substrate/common electrode 15 having an ITO layer 16 interposed thereon is formed on an opposite substrate 17. Glass substrate 1 manufactured by the above-described steps is assembled with the opposite substrate 17. The liquid crystal 14 is injected between the color filter substrate/common electrode 15 and the opposite substrate 17. The subcomponents of the LCD panel or module, that is, the peripherals such as the CPU, RAM, ROM, IC, resistors, capacitors, oscillators, connectors and the like, found on the bare chip 11, are fixed to the mounting pad 8. Wires 10 are connected to each successive chip in a process of molding involving resin 12. Finally, polarizing plates 13 and 18 which either transmits or absorbs a specific component of polarized light 13 and 18 are provided.
In the related art described above, after forming the CPU circuit and the controller by a separate semiconductor process, on a wafer of single crystalline silicon, the CPU circuit and the controller consisting of a CPU, RAM, ROM, IC, resistors, capacitors, oscillators, connectors, are attached to a panel of the LCD in order to fabricate an SOP typed LCD.
In the prior art techniques discussed so far, each integrated circuit IC chip (hereinafter IC chip) in a controller and a CPU circuit is fabricated on a silicon wafer by a general semiconductor fabrication process and then subsequently attached to a glass substrate since the controller and the CPU circuit are formed with single crystalline silicon. Accordingly, the process of fabricating pixels and LCD drivers are kept separate from other processes for fabricating the controller and the CPU circuit. The SOP typed LCD manufactured by the foregoing technique reaches the limits of lightness and product miniaturization since the controller and CPU circuit occupy a certain space.